Park Highlights

USGS Geology

NRCS Soils

Richmond

National Battlefield Park

Virginia

Ricmond National Battlefield Park, Virginia

All of the park units lie within the Atlantic Coastal Plain Physiographic Province,
immediately east of the transition zone (the Fall Line) between the Piedmont and Atlantic
Coastal Plain Physiographic provinces. The Fall Line, which separates the two
physiographic provinces, trends roughly north to south in this area. The Atlantic Coastal
Plain Physiographic Province (hereinafter referred to as the Coastal Plain) comprises
approximately 10,000 mi2 in Virginia.

The Coastal Plain consists of Cretaceous- through Quaternary-age sediments that thicken
eastward; at the Fall Line, the sediments are very thin, whereas at the Atlantic Ocean
coastline, the sediments are over 5,000 feet thick (Meng and Harsh 1988). In general,
Coastal Plain sediments consist of unconsolidated interbedded gravels, sands, silts, and
clays (Meng and Harsh 1988).

The geology of the Richmond and Seven Pines 1:24,000-scale topographic quadrangles
has been mapped by Daniels and Onuschak (1974), providing detailed mapping for the
Beaver Dam Creek, Chickahominy Bluff, Cold Harbor, and Gaines' Mill units.
Additional details on the geology of the Cold Harbor unit can be found in Inners et al.
(1995). Detailed geologic mapping (at a scale of 1:24,000) does not exist for the
Drewry's Bluff, Dutch Gap, or Roxbury topographic quadrangles, which encompass the
Drewry's Bluff, Fort Harrison, and Malvern Hill/Glendale units, however some details on
the geology of the Drewry's Bluff and Fort Harrison units can be found in Inners et al.
(1995). Less detailed geologic mapping for the Drewry's Bluff, Fort Harrison, and
Malvern Hill/Glendale units exists at a scale of 1:250,000 (Mixon et al. 1989).

The Beaver Dam Creek unit is predominantly underlain by recent alluvium of Beaver
Dam Creek (Daniels and Onuschak 1974). The majority of this alluvium consists of
organic and poorly sorted deposits ranging from clay to gravel (Daniels and Onuschak
1974). Older (Tertiary) clayey silt deposits are exposed along the eastern and western
boundaries of the unit (Daniels and Onuschak 1974). Mixon et al. (1989) mapped this
area as the Late Tertiary Chesapeake Group.

Three geologic units are exposed in the Chickahominy Bluff park unit. The highest
elevations are underlain by undivided Late Tertiary - Early Quaternary upland sand and
gravel deposits (Daniels and Onuschak 1974). The bluff is cut into underlying clayey silt
deposits, also of Late Tertiary - Early Quaternary age, and the bottomlands are underlain
by more recent alluvial deposits of the Chickahominy River (Daniels and Onuschak
1974). Mixon et al. (1989) mapped the clayey silt deposits as the Late Tertiary
Chesapeake Group.

The Fort Harrison unit is underlain by the Quaternary-age Windsor Formation and the
Tertiary age Bacon's Castle Formation (Mixon et al. 1989). The Windsor Formation
consists of sand, gravel, silt, and clay (Mixon et al. 1989) with some glauconite (Inners et
al. 1995). The Bacon's Castle Formation is subdivided and mapped as two units. The
unit underlying the Fort Harrison unit is characterized by thick-bedded gravel, grading
upward into sand and sandy and clayey silt (Mixon et al. 1989).

The Bacon's Castle Formation, as described above for the Fort Harrison unit underlies
the higher elevations of the Malvern Hill and Glendale units. The Chesapeake Group is
exposed on the steep slopes on the west side of the battlefield and on the slopes on the
east side of the battlefield along Western Run (Mixon et al. 1989). The extreme western
edge of the battlefield unit is underlain by the middle Pleistocene-age Chuckatuck
Formation, a geologic unit containing sand, silt, and clay, with minor amounts of peat
(Mixon et al. 1989).

Hydrogeology

The regional hydrogeology of the Coastal Plain Physiographic Province is controlled by
the configuration of the Coastal Plain sediments, i.e., the sediments are interbedded in a
more or less regular sequence of layers of high permeability alternating with layers of
low permeability. The layers of high permeability, which are generally composed of
sand and sandy sediments, transmit ground water readily and are known as aquifers. An
aquifer is defined as a water-bearing geologic unit. The layers of low permeability,
which are generally composed of clay and clayey sediments, do not transmit ground
water readily and are called confining units, or aquitards. Aquifers that are located
beneath or between aquitards are termed confined aquifers.

The surficial aquifer is composed of permeable geologic materials and extends downward
from elevations at or near land surface to the top of the uppermost aquitard, or to bedrock
along the western edge of the Coastal Plain. Because there is no upper confining unit, it
is called an unconfined aquifer. This shallow ground water in the surficial aquifer
supplies most of the water by seeps and springs to small streams and many wetlands.
The top of the saturated zone, called the water table, is free to rise in response to recharge
(i.e. precipitation) and fall in response to discharge (i.e. from drawdown induced by
pumping from wells completed in the surficial aquifer, or by supplying water to streams).
Pumping from wells completed in confined aquifers affects water levels in those aquifers
to a greater extent than the affect on water levels in the surficial aquifer by pumping in
wells completed there. In this report, water in a confined aquifer is referred to as deep
ground water, and water in the surficial aquifer is referred to as shallow ground water. A
generalized hydrogeologic section and direction of ground-water flow in the Coastal
Plain Physiographic Province of Virginia (McFarland 1997) is shown in Figure 10.

The Beaver Dam Creek unit is underlain by bedrock at an estimated depth of 200 to 250
feet below sea level (Meng and Harsh 1988). The unconsolidated Potomac Formation
sediments above the bedrock form a probable unconfined aquifer, though some confined
or semi-confined zones within the Potomac Formation sediments may exist at depth.
Depth to ground water is consistently shallow, as this area serves as a ground-water
discharge zone.

The Chickahominy Bluff unit is underlain by bedrock at a depth probably in the range of
100 to 200 feet below sea level (Meng and Harsh 1988). The unconsolidated Potomac
Formation sediments above the bedrock form a probable unconfined aquifer. Ground
water likely flows north and east towards the Chickahominy River. Depth to ground
water is variable, on the basis of the variable topography.

The Drewry's Bluff unit is underlain by approximately 150 feet of unconsolidated
sediment, which likely is an unconfined aquifer. In the higher elevations of the unit, from
land surface, the first 10 feet consists of a shallow capping unit, probably Pleistocene-age
sand and gravel (Inners et al. 1995). Underlying this capping unit is a thicker sequence
of the Potomac Formation, which extends to the top of basement rock (Meng and Harsh
1988). Basement rock (probably the Petersburg Granite, Inners et al. 1995) is at a depth
of approximately 55 feet below sea level (Meng and Harsh 1988). On the basis of the
variable topography, depth to ground water at this site is highly variable. In general, the
water table is deepest beneath the higher elevations along the river and shallower along
the western edge of the unit and in the deep erosive cuts. Ground water movement is
likely eastward towards the James River.

The Fort Harrison unit is underlain by basement rock at a depth of approximately 75 to
125 feet below mean sea level. The Lower Potomac Aquifer is partially present but
probably does not attain its full thickness; it is unknown whether or not it is fully
confined. The Lower Potomac confining unit may be partially present and is probably
less than 20 feet thick (Meng and Harsh 1988). The Middle Potomac Aquifer is likely
discontinuous and not of its full thickness; the altitude of the top of this aquifer is
approximately 35 to 55 feet above mean sea level (Meng and Harsh 1988). The thickness
of the Middle Potomac confining unit is approximately 20 feet (Meng and Harsh 1988).
Sediments comprising the Aquia Aquifer, the Nanjemoy-Marlboro clay confining unit,
the Calvert confining unit, and the Yorktown-Eastover Aquifer are likely present in the
subsurface over portions of the unit, but if present below the local ground-water table,
they may not occur in the distinct and orderly sequence in which they occur farther to the
east. The condition of these formations, with respect to whether they occur as confined,
semi-confined, or unconfined aquifers, is unknown. Two wells, however, are reportedly
screened in the Yorktown-Eastover and the Aquia aquifers (White et al. 2001); see
section on Ground-Water Resources of the Fort Harrison unit.

The Malvern Hill and Glendale units are underlain by basement rock at a depth of
approximately 250 to 400 feet below mean sea level. The altitude of the top of the Lower
Potomac Aquifer is approximately 200 to 300 feet below mean sea level (Meng and
Harsh 1988). The thickness of both the Lower Potomac and the Middle Potomac
confining units is approximately 15 to 20 feet (Meng and Harsh 1988). The altitude of
the top of the Middle Potomac Aquifer is approximately 50 to 90 feet below mean sea
level (Meng and Harsh 1988). The altitude of the top of the Aquia Aquifer, which may
be confined, partially confined, or unconfined across the unit, is approximately 10 to 40
feet below mean sea level (Meng and Harsh 1988). The thickness of the Nanjemoy-
Marlboro clay confining unit is approximately 20 feet (Meng and Harsh 1988).
Sediments comprising the Chickahominy-Piney Point Aquifer, the Calvert confining unit,
and the Yorktown-Eastover Aquifer may be present in the subsurface over portions of the
unit, but if present below the local ground-water table, they may not occur in the distinct
and orderly sequence in which they occur farther to the east. The condition of these
formations, with respect to whether they occur as confined, semi-confined, or unconfined
aquifers, is unknown.

Topography and Soils

Topography of the Coastal Plain Physiographic Province in general is characterized by
large, relatively level terraces or plateaus. These upland areas are bounded by steep
embankments that form the margins of waterways. Waterways are typically edged by
swamps and other wetlands over much of their floodplains.

Topography in most of the park units is gently rolling and locally incised by streams; the
exceptions are at Chickahominy Bluff and Drewry's Bluff, which have steep bluffs, and
Malvern Hill, which has moderately steep slopes. Of the units addressed in this report,
the minimum elevation is less than 10 feet (at the James River) in the Drewry's Bluff
unit, and the maximum elevation is 185 feet in the Cold Harbor unit. The range in
elevation for each unit shows that the Beaver Dam Creek unit has the flattest topography.

Hodges (1978) mapped soils in Chesterfield County. In general, soils in the Drewry's
Bluff unit are on uplands and are of the Gritney-Atlee-Lenoir association, which is
characterized as deep, well drained to somewhat poorly drained soils, having a clayey or
loamy subsoil. Specific details on the soils underlying each unit are shown in Table 2.

Hodges et al. (1980) mapped soils in Hanover County. The soils underlying the Beaver
Dam Creek, Cold Harbor, and Gaines' Mill units are classified as Coastal Plain soils, and
include the Udults-Ochrepts-Suffolk association, the Ochrepts-Udults-Kempsville
association, the Norfolk-Caroline-Dogue association, and the Norfolk-Orangeburg-
Faceville association. These four soil associations are in general deep, moderately well
to well drained and have a subsoil that is dominantly sandy, loamy, or clayey. These
soils generally are found on uplands.

Clay (1975) mapped soils in Henrico County. The soils underlying the Chickahominy
Bluff, Fort Harrison, Malvern Hill, and Glendale units are of the Kempsville-Atlee-
Duplin association, the Ochrepts and Udults-Norfolk-Caroline association, or the Angie-
Pamunkey-Lenoir association. These three soil associations are in general deep and well
drained, some with gravel, some with a fragipan, and some poorly drained. These soils
generally are found on uplands and stream terraces.

The spectacular geology in our national parks provides the answers to many
questions about the Earth. The answers can be appreciated through plate tectonics,
an exciting way to understand the ongoing natural processes that sculpt our
landscape. Parks and Plates is a visual and scientific voyage of discovery!

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